We know little about projections of the primate cerebellar cortex, and almost no attempt has been made to correlate the evolution of primate locomotor styles with specializations of cerebellar connectivity. This study will address these points. The primary animal models utilized are the lesser bushbaby (Galago senegalensis) a Lorisoid primate with a unique locomotor style and the tree shrew (Tupaia glis) a generalized quadrupedal mammal considered to be the best extant example of the Paleocene forms from which primates evolved. Cerebellar corticonuclear connections will be analyzed in detail using the Fink-Heimer selective silver impregnation method. Special attention is directed to the topographical representation of the cortex in the deep nuclei and the organization of zones in the cortex as reflected by the arrangement of this fiber system. Using horseradish peroxidase (HRP) as a retrograde tracer, the location and organization of nucleocortical cells will be ascertained. Emphasis will be placed on their topographical relationship with the ipsilateral cortex, and on the distribution of recently discovered contralateral nucleocortical cells. Cerebellar nuclear efferent projections to select brainstem relay nuclei (e.g. red nucleus, vestibular nuclei, pontine nuclei) will be studied using both anterograde and retrograde tracing techniques. The anterograde course and termination of spinocerebellar fibers in sagittally oriented laminae in the granular layer of cerebellar cortex will be determined using Fink-Heimer method. An integral part of this proposal is a series of Golgi studies which will elucidate the cytoarchitecture of terminal nuclei. The results will be considered in light of the phylogenetic level and locomotor style of each species and current theories concerning locomotor evolution in primates.